Space syntax is a set of methods and theories that study how the configuration structure of space, organization, and social behaviors interact. Examining the spatial layout is one of the basic strategies for evaluating the usages of any building. This issue is especially evident in historical buildings because the technique of space syntax and drawing justification diagrams makes it possible to analyze the spatial relationships of buildings. Shah Abbasi Caravanserai has long centuries history and has had different uses in different periods. This article examines the spatial arrangement of Shah Abbasi Caravanserai, located in Karaj, in the Safavid and Qajar periods by using the space syntax technique. Also, by considering the change of Shah Abbasi Caravanserai's use to a school in the Qajar period, it seeks to answer the main question: to what extent did the new use correspond to the spatial relations of Shah Abbasi Caravanserai? What are the advantages and disadvantages of changing this user? To answer this question, first, using the descriptive-analytical method and library studies and field surveys, the spatial arrangement of Shah Abbasi Caravanserai in the Safavid and Qajar periods has been studied. Then, drawing diagrams using the space syntax technique and analyzing them based on various influential factors was done. The research result was concluded through analyzing data and comparing the justification diagrams with school diagrams in the Qajar period, indicating that the new spatial arrangement of Shah Abbasi Caravanserai in the Qajar era was done as a result of changing the use to the school. Also, despite some disadvantages because of this change, including a lack of attention to proper access hierarchy, ventilation, and proportions, it is compatible with the spatial relationships of schools of that time to a large extent.